Characterizing the role of MSRA in pancreatic tumorigenesis

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PROJECT SUMMARY Pancreatic ductal adenocarcinoma (PDA) is an aggressive malignancy that remains largely incurable. The KRAS oncogene is mutated in 95% of PDAs and acts as a potent driver of PDA growth and maintenance. Oncogenic KRAS induces a profound rewiring of metabolic pathways that are essential for PDA growth. Interestingly, this rewiring generates metabolic by-products, including reactive oxygen species (ROS), that can potentially oxidize macromolecules, resulting in genomic instability and toxic cellular damage. However, in addition to these indiscriminate activities, ROS can also initiate redox signaling through oxidative post-translational modifications of proteinaceous cysteines, such that toggling between the reduced and oxidized states of cysteine constitutes a “redox switch” that can regulate the structure and/or function of a protein. Indeed, using our pancreatic organoid model (Cell, 2015), we previously showed that oncogenic KRAS promotes pancreatic tumorigenesis in part by regulating the cyclic reduction/oxidation of cysteines on select proteins involved in the translation machinery (Cell, 2016), thereby promoting protein synthesis (Cell, 2016), glucose metabolism, and tumor growth (Nature Communications, 2019). While cysteine is well-recognized for its susceptibility to oxidation, it is often not appreciated that methionine, the other sulfur-containing amino acid, can be readily oxidized to methionine sulfoxide, and reduced by the oxidoreductase, methionine sulfoxide reductase A (MSRA). Using a tissue microarray of patient-derived pancreatic tumors and adjacent normal tissues, we observed a stage-dependent decrease in MSRA protein expression in tumor tissues. Consistently, acute knockout of murine MSRA using CRISPR/Cas9 in premalignant pancreatic organoids provides a migratory advantage in vitro and in vivo. Thus, we hypothesize that redox signaling through oxidative post-translational modification of methionine residues (Met-oxPTM) represents an unexplored mechanism that supports pancreatic metastasis. Herein, we propose to i) define the mechanism regulating MSRA expression in PDA, ii) characterize the functional and clinical significance of oxidized methionine peptides in PDA metastasis, and iii) define and characterize targetable vulnerabilities created by Met-oxPTM in PDA cells.